Hilchos Lashon Hara, chapter 3, section 3

The prohibition of lashon hara applies even if does is not speaking out of hatred and has no intent to denigrate him, but is speaking in jest and levity. Even so, because what he is saying is derogatory, it is forbidden by the Torah.

The Chofetz Chaim

Rav Yisroel Meir Hakohen of Radin zt"l known as the Chofetz Chaim, was one of the most famous rabbis before the Holocaust.
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